Driver of piezoelectric actuator

ABSTRACT

To make it possible to sustain a low power consumption for the entire driver in a driver of a piezoelectric actuator, by reducing the number of components and switching the piezoelectric actuator at a high speed. Common resistors Ra and Rb for current limitation are interposed at some midpoint of the feeder lines  19  and  21 . Phototransistors Q 1  to Q 8  are connected to the power source side of the common resistors Ra and Rb of the feeder lines  19  and  21 . Piezoelectric actuators  1   a  to  1   h  are connected to terminals Sa and Sb of the common resistors Ra and Rb on the side opposite to the power supply section, and to the joints of the phototransistors Q 1  to Q 8 . Light emitting diodes D 1  to D 8  are disposed in proximity to the phototransistors Q 1  to Q 8 , and the light emitting diodes D 1  to D 8  are switched and conducted at a switching control section  25 . The switching control section  25  overlaps conduction control of the light emitting diodes D 1  to D 8  corresponding to the next piezoelectric actuators  1   a  to  1   h , after the 70% charged state of the piezoelectric actuators  1   a  to  1   h  in association with the on-operation of the piezoelectric actuators  1   a  to  1   h.

TECHNICAL FIELD

The present invention relates to a driver of a piezoelectric actuator,and particularly to improvement in the driver of the piezoelectricactuator for driving a plurality of piezoelectric actuators mechanicallymoving each of the plural mechanism components directly or indirectlyinstalled on the driver, by switching them.

BACKGROUND ART

Conventionally, as shown in FIG. 5, a piezoelectric actuator 1 isconstituted in such a manner that thin piezoelectric plates 5 and 7 arestuck to opposing faces of rectangular conductive plates 3, andelectrodes 5 a and 7 a are disposed on the opposing faces which are notbrought into contact with the plates 3 in each piezoelectric plate 5,with the plates 3 serving as common electrodes, and while supporting oneend (left end in the figure) in the longitudinal directions of theplates 3 in an open-sided shape, the other end (right end in the figure)is formed in an open end. Note that a support member of thepiezoelectric actuator 1 is not shown in FIG. 5 (see FIG. 6).

In the piezoelectric actuator 1, for example, when positive potential+isapplied between a positive terminal P1 and a common terminal P3 (betweenthe electrode 5 a of the piezoelectric plate 5 and the plate 3)according to the polarization directions of the piezoelectric plates 5and 7, for example, the plate 3 is bent so that the open end isdisplaced in the upward direction as shown by broken line in FIG. 5.

Meanwhile, when a negative potential—is applied between the commonterminal P3 and a negative terminal P2 (between the plate 3 and theelectrode 7 a of the other piezoelectric plate 7), for example, the openend is displaced in the downward direction as shown by one-dot chainline in the figure.

Then, the piezoelectric actuator 1 is used as various driving sources,such as a needle selecting driver of knitting needles of a knittingmachine, by utilizing a bending motion by dint of such a piezoelectricphenomenon.

Specifically, as shown in FIG. 6, the aforementioned pluralpiezoelectric actuators 1 (shown by dividing into 1 a, 1 b, 1 c, 1 d, 1e, 1 f, 1 g, and 1 h in the figure) are arranged on a side wall 9 a in along and narrow insulating box-shaped case 9 in parallel to each otherat prescribed intervals apart from one another, with the one endsupported in an open-sided shape and the other end as the open endinserted into operation holes 11 formed on the side wall 9 b opposing tothe side wall 9 a in the case 9 with a certain play. Then, operationpieces 13 as mechanical components fixed to the other ends are protrudedwith a certain play from the operation holes 11.

A plurality of piezoelectric actuators 1 a to 1 h (including theoperation pieces 13) supported by the case 9 are the same actuators, andFIG. 7 is a view of the case 9 viewed from the side of the side wall 9 bof the case 9, specifically from tip end sides of the operation pieces13.

When a positive/negative direct current drive voltage is applied from apower supply section 15 to such plural piezoelectric actuators 1 a to 1h through a controller 17, each of the piezoelectric actuators 1 a to 1h is bent and the operation pieces 13 protruding from the operationholes 11 of the case 9 are displaced. This contributes to moving aselecting needle lever not shown (mechanism component) by the operationpieces 13.

Then, when the controller 17 switches and selects the drive voltageapplied to the plural piezoelectric actuators 1 a to 1 h, thepiezoelectric actuators 1 a to 1 h can be used as a needle selectingdriver of the knitting needles of the knitting machine, for example.

A general patent document according to such a kind of piezoelectricactuator includes a patent document 1 (Japanese Patent Laid OpenNo.5-302251).

Further, the structure as shown in FIG. 8 is given as an example of thestructure of controlling the drive voltage applied to the pluralpiezoelectric actuators 1 a to 1 h by the controller 17.

Specifically, phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, Q7 andQ8, which are connected in series respectively, are disposedcorresponding to the plural piezoelectric actuators 1 a to 1 h. Acollector of one of the phototransistors Q1 is connected tophototransistors Q1 and Q2 through a resistor R1 from a positive sidefeeder line 19, and an emitter of the other phototransistor Q2 isconnected to a negative side feeder line 21 through a resistor R2.

The positive terminal P1 in the piezoelectric actuator 1 a is connectedto the positive side feeder line 19, the negative terminal P2 isconnected to the negative side feeder line 21, and joints of thephototransistors Q1 and Q2 are connected to common terminal P3 of thepiezoelectric actuator 1 a.

Similarly, the phototransistors Q3 to Q8 are also connected to thepositive side and negative side feeder lines 19 and 21 through resistorsR3 to R8, and the piezoelectric actuators 1 b to 1 d are also connectedto the joints of the phototransistors Q3 to Q8 and the positive side andnegative side feeder lines 19 and 21.

In addition, light emitting diodes D1 and D2, D3 and D4, D5 and D6, andD7 and D8 are disposed in proximity to and corresponding to the phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8 connected inseries.

The light emitting diodes D1 to D8 are emitted by selectively energizingby a switching control section 23, and the driver of the aforementionedpiezoelectric actuators is thereby formed.

In FIG. 8, the aforementioned controller 17 is formed by thephototransistors Q1 to Q8, light emitting diodes D1 to D8, and theswitching control section 23.

Note that in FIG. 8, the light emitting diodes D1 to D8 are connected byone line from the switching control section 23. However, actually thelight emitting diodes D1 to D8 are connected by individual wiringcorresponding to the light emitting diodes D1 to D8. Such wiring issimplified in FIG. 8 so as to be easy to understand.

Then, for example, when the piezoelectric actuator 1 a out of the pluralpiezoelectric actuators 1 a to 1 d is on-operated, the open end isdisplaced in the upward direction through the conduction control of onlylight emitting diode D1 selectively by the switching control section 23.Meanwhile, the tip end is displaced in the downward direction throughthe conduction control of only light emitting diode D2 selectively.

Similarly, in the other piezoelectric actuators 1 b to 1 d also, the tipend is displaced through the conduction control of only either of thelight emitting diodes D3 or D4, D5 or D6, and D7 or D8.

In the driver of the piezoelectric actuators thus constituted, theresistors R1 to R8 connected between the phototransistors Q1 to Q8 andthe positive side and negative side feeder lines 19 and 21 have acurrent limit function to suppress a drive current flowing through thephototransistors Q1 to Q8 so as not to increase the power consumptionfor the entire driver due to increased drive current, which occurs whenone of the phototransistors is switched to the other in thephototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8, therebycausing both of the phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6,and Q7 and Q8 to be temporarily conducted or a rapid current change tooccur, resulting in a large drive current.

However, in the driver of the aforementioned piezoelectric actuators,the resistors R1 to R8 for current limitation are connected to theplural phototransistors Q1 to Q8 to on-drive the plural piezoelectricactuators 1 a to 1 h. Therefore, the number of components is increased,the wiring is complicated, a cost is difficult to be reduced, andproductivity is also difficult to be improved.

In such a condition, it is considered that if the resistors for currentlimitation are inserted in the parts up to the controller 17 one by onein the positive side and negative side feeder lines 19 and 21, thenumber of components is reduced, and the wiring is simplified. However,this is not realized for the reason described hereunder.

More specifically, in the piezoelectric actuators 1 a to 1 h of thiskind used for the needle selecting driver of the knitting needle of theknitting machine or the like, a quick switching speed allows theknitting needle to be quickly displaced, thereby increasing a knittingspeed.

For example, when the piezoelectric actuator 1 a is on-controlled andanother piezoelectric actuator 1 b is on-controlled at the same time orimmediately following, or when the piezoelectric actuators 1 a to 1 hare sequentially on/off controlled while on/off operation switchingtiming is reduced, a large drive current flows temporarily. Under such asituation, if one or a pair of resistors R for current limitation areprovided, heat generation is apt to be large.

In order to avert above-described situation, a large power consumptionand an expensive resistor are needed, and consequently, inexpensiveresistors R1 to R8 with low power consumption are inserted and connectedfor each of the piezoelectric actuators 1 a to 1 h.

The inventors of the present invention carefully study on the functionand an equivalent circuit of the piezoelectric actuators 1 a to 1 h. Asa result, the inventors of the present invention focus on the point thatthe piezoelectric actuators 1 a to 1 h have a function as capacitorsequivalently, and the drive current flowing through the piezoelectricactuators 1 a to 1 h is reduced in accordance with the progress ofcharging operation, although large immediately after the on-control, andafter a specified period has passed, the drive current becomes verysmall, and the change with the lapse of time is small. Consequently itis found that the number of the resistors is reduced and thepiezoelectric actuators 1 a to 1 h can be switched at a high speed, andthe present invention is thus completed.

In order to solve the above-described problem, an object of the presentinvention is to provide a driver of a piezoelectric actuator capable ofreducing in the number of resistors suppressing increase in a drivecurrent and switching plural piezoelectric actuators at a high speed andsustaining low power consumption for the entire driver in the driver fordriving the plural piezoelectric actuators.

DISCLOSURE OF THE INVENTION

In order to solve the aforementioned problem, the present inventionprovides the plural actuators in which the piezoelectric plates arestuck to the plates, comprising:

plural actuators mechanically moving a mechanical component directly orindirectly connected to each of the piezoelectric actuators;

feeder lines extending from a power supply section for applying a drivevoltage to the piezoelectric plate of each of the piezoelectricactuators;

common resistors connected to the feeder lines in series for currentlimitation limiting the drive current to the piezoelectric plate of thepiezoelectric actuators to a prescribed range; and

a controller sequentially selectively on-controlling the drive voltageapplied to the piezoelectric plate of each of the piezoelectricactuators by the feeder lines.

In addition, the plural piezoelectric actuators are connected to thefeeder lines of the common resistors on the side opposite to the powersupply section, and the controller has a function to on-control thedrive voltage to be applied to the piezoelectric plate of thepiezoelectric actuator to be driven next, after the piezoelectric plateof the piezoelectric actuator, to which the drive voltage is applied, isput into a 60% or more charged state.

Further, according to the present invention, the controller can alsohave the function to on-control the drive voltage to be applied to thepiezoelectric plate of the piezoelectric actuator to be driven next,during applying the drive voltage to the piezoelectric plate of thepiezoelectric actuator to which the drive voltage is applied.

Also, according to the present invention, preferably, the controller isconnected to the power section side of the common resistors, and thedrive voltage applied to the piezoelectric plates of piezoelectricactuators is on-controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block circuit diagram showing an embodiment relating to adriver of a piezoelectric actuator according to the present invention.

FIG. 2 is a view showing an example of a charging characteristic of thepiezoelectric actuator.

FIG. 3 is a waveform chart explaining a switching operation of thedriver of the piezoelectric actuator according to the present invention.

FIG. 4 is a block circuit diagram showing other embodiment relating tothe driver of the piezoelectric actuator according to the presentinvention.

FIG. 5 is a sectional view showing a general configuration of thepiezoelectric actuator.

FIG. 6 is a sectional view showing a configuration example utilizing thepiezoelectric actuator.

FIG. 7 is a side view of an essential part of FIG. 6.

FIG. 8 is a block circuit diagram showing the driver of the conventionalpiezoelectric actuator.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained with reference tothe drawings of the present invention hereunder. Note that the partsidentical to those in the conventional example are assigned the samenumerals without further explanation.

FIG. 1 is a block diagram showing an embodiment relating to a driver ofa piezoelectric actuator according to the present invention.

In FIG. 1, plural piezoelectric actuators 1 a, 1 b, 1 c, 1 d, 1 e, 1 f,1 g, and 1 h are constituted, as shown in FIG. 5 for example, bypiezoelectric plates 5 and 7 stuck to opposing faces of the conductiveplates 3, and electrodes 5 a and 7 a disposed on the opposing faceswhich are not brought into contact with the plate 3 of each of thepiezoelectric plates 5 and 7, with the plates 3 serving as commonelectrodes of each of the piezoelectric plates 5 and 7, and as shown inFIG. 6, supported by a box-shaped case 9 (not shown in FIG. 1) in anopen-sided shape.

Note that in FIG. 1, the piezoelectric actuators 1 d to 1 g are notshown, however they are formed in the same way as the piezoelectricactuators 1 a, 1 b, and 1 c.

As shown in FIG. 6, a positive side feeder line 19 and a negative sidefeeder line 21 are extended from a power supply section 15, serving aslines to supply a positive DC power source of about +50V to +100 V, anda negative DC power source of about −50V to −100V, with common resistorsRa and Rb for current limitation inserted and connected in series in themiddle thereof.

Phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8 in whichemitters and collectors are mutually connected in series, are disposedcorresponding to the piezoelectric actuators 1 a to 1 h.

Each collector of each of the phototransistors Q1, Q3, Q5, and Q7 isdirectly connected to the positive side feeder line 19 on the side ofthe power supply section of the common resistor Ra, not through thecommon resistor Ra.

Each emitter of the phototransistors Q2, Q4, Q6, and Q8 is connected tothe negative side feeder line 21 on the side of the power supply sectionof the common resistor Rb.

Joints of the phototransistors Q1 and Q2, Q3 and Q4, and Q7 and Q8 areconnected to common terminals P3 of the piezoelectric actuators 1 a, 1b, 1 c, to 1 h.

Positive terminals P1 of the piezoelectric actuators 1 a, 1 b, 1 c, to 1h are connected to terminal Sa of the common resistor Ra of the positiveside feeder line 19 on the side opposite to the power supply section,and negative terminals P2 of the piezoelectric actuators 1 a, 1 b, 1 cto 1 h are connected to a terminal Sb of the common resistor Rb of thenegative side feeder line 21 on the side opposite to the power supplysection.

Light emitting diodes D1 and D2, D3 and D4, D5 and D6, and D7 and D8 aresequentially connected in series.

The light emitting diode D1 and the phototransistor Q1, the lightemitting diode D2 and the phototransistor Q2, the light emitting diodeD3 and the phototransistor Q3, the light emitting diode D4 andphototransistor Q4, the light emitting diode D5 and phototransistor Q5,the light emitting diode D6 and the phototransistor Q6, the lightemitting diode D7 and the phototransistor Q7, and the light emittingdiode D8 and the phototransistor Q8, are correspondingly disposed inproximity to each other, respectively.

The light emitting diodes D1 and D2, D3 and D4, D5 and D6, and D7 and D8are connected to a switching control section 25. Then, by this switchingcontrol section 25, any one of the light emitting diodes D1 to D8 isswitched and conducted to emit light.

Note that in FIG. 1 also, the light emitting diodes D1 to D8 areconnected by one line from the switching control section 25. However, inthe same way as explained in FIG. 8, actually the light emitting diodesD1 to D8 are connected by individual wiring corresponding to the lightemitting diodes D1 and D2, D3 and D4, D5 and D6, and D7 and D8, therebyperforming emission control by selecting any one of the light emittingdiodes D1 to D8, in the same way as shown in FIG. 8.

For example, when only light emitting diode D1 is selectively switchedand conducted at the switching control section 25, the phototransistorQ1 is on-operated by receiving the light from the light emitting diodeD1, and the positive drive current is applied to both sides of thepiezoelectric plate 5 (not shown in FIG. 1) of the piezoelectricactuator 1 a. Meanwhile, the negative drive voltage is applied to bothsides of the piezoelectric plate 7 (not shown in FIG. 1) of thepiezoelectric actuator 1 a which is thereby charged, and the open endthereof (operation piece 13) is thereby displaced in the upwarddirection.

When the light emitting diodes D1 and D3 are selectively switched andconducted at the switching control section 25, the phototransistors Q1and Q3 are on-operated, and the open ends (operation pieces 13) of thepiezoelectric actuators 1 a and 1 b are displaced in the upwarddirection.

Then, the plural light emitting diodes D1 to D8 are sequentiallyselectively controlled and conducted at the switching control section25.

More specifically, for example, as shown in FIG. 3, the switchingcontrol section 25 functions to on-control the drive voltageapplication, so that the drive voltage is applied to the pluralpiezoelectric actuators 1 a to 1 h in such a manner that the drivevoltage is applied to the piezoelectric actuator 1 a, subsequentlyapplied to the piezoelectric actuator 1 b, and then applied to 1 c to 1h in this order.

Further, when the piezoelectric actuator 1 a (correctly piezoelectricplates 5 and 7) is put into 70% charged state, the drive voltage appliedto the next piezoelectric actuator 1 b is on-controlled, and when thedrive voltage applied to the piezoelectric actuator 1 b is put into the70% charged state, the drive voltage applied to the next piezoelectricactuator 1 c is further on-controlled. Thereafter onward, the control ofthe drive voltage is sequentially repeated.

FIG. 2 shows a change of charging with lapse of time, wherein when thedrive voltage is applied to each of the piezoelectric actuators 1 a to 1h up to the point T of 70% charged state, the drive voltage iscontrolled and started to be applied to the next piezoelectric actuators1 a to 1 h.

After the lapse of time (for example, 200μ seconds) of applying thedrive voltage to each of the piezoelectric actuators 1 a to 1 h,individual or all drive voltage is off-controlled at the switchingcontrol section 25.

Accordingly, each of the piezoelectric actuators 1 a to 1 h is designedso that the switching control section 25 overlaps conduction control ofeach piezoelectric actuator 1 a to 1 h sequentially during the timeperiod from the drive voltage is put into the 70% charged state untilthe application of the drive voltage is off-controlled, and thepiezoelectric actuators 1 a to 1 h are increased through such overlappedconduction control.

The designation mark 27 in FIG. 1 indicates the controller constitutedof the aforementioned phototransistors Q1 to Q8, the light emittingdiodes D1 to D8, and the switching control section 25, the switchingcontrol section 25 having the function to selectively switch and controlthe drive voltage applied to the piezoelectric plate of each of thepiezoelectric actuators 1 a to 1 h sequentially from the feeder lines 19and 21.

Next, brief explanation will be given to the driver of the piezoelectricactuators thus constructed, in a case of on-operating the piezoelectricactuators 1 a to 1 h sequentially in this order, for example.

When the switching control section 25 selectively performs theconduction control of only light emitting diode D1, the phototransistorQ1 is on-operated, and the positive side drive voltage is applied fromthe feeder line 19 to the piezoelectric actuator 1 a through the commonresistor Ra, and the open end thereof is displaced in the upwarddirection.

The switching control section 25 performs the conduction control of thelight emitting diode D3 also after the 70% charged state of thepiezoelectric actuator 1 a, and the phototransistor Q3 is therebyon-operated.

Therefore, the positive side drive voltage is applied from the feederline 19 to the piezoelectric actuator 1 b through the common resistorRa, and the open end thereof is also displaced in the upward direction.

In this case, as shown in FIG. 3, at operation start time of thepiezoelectric actuator 1 b, which is bend-driven after delay, thebend-drive of the piezoelectric actuator 1 a previously startedoperating is also going on.

When the piezoelectric actuator 1 b is put into the 70% charged state,the conduction of the light emitting diode D5 is on-controlled at theswitching control section 25 and the phototransistor Q5 is off-operated,the piezoelectric actuator 1 c is also bend-driven in an overlappingmanner. Thereafter, this process is repeated.

In this way, the driver of the piezoelectric actuator of the presentinvention is constituted by inserting and connecting the commonresistors Ra and Rb for current limitation in series at some mid pointof the positive side and the negative side feeder lines 19 and 21,connecting one end of the phototransistors Q1, Q3, Q5, and Q7 to thepower supply section side of the common resistor Ra of the positive sidefeeder line 19, and connecting one end of the phototransistors Q2, Q4,Q6, and Q8 to the power supply section side of the common resistor Rb ofthe negative side feeder line 21 out of the phototransistors Q1 and Q2,Q3 and Q4, Q5 and Q6, Q7 and Q8 connected in series corresponding to theplural piezoelectric actuators 1 a to 1 h, and connecting the commonterminals P3 of the piezoelectric actuators 1 a, 1 b, 1 c to 1 h to thejoints of the phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, Q7 andQ8, and further connecting the positive terminal P1 and the negativeterminal P2 to the positive side and the negative side feeder lines 19and 21 through the terminals Sa and Sb of the common resistor Ra on theside opposite to the power supply section.

Then, the light emitting diodes D1 to D8 are disposed in proximity tothe phototransistors Q1 to Q8 corresponding thereto. Particularly, theswitching control section 25 has the function to conduction control ofany one of the light emitting diodes D1 to D8 to control the drivevoltage to be applied to the corresponding piezoelectric actuators 1 ato 1 h, and overlap conduction control of the light emitting diodes D1to D8 corresponding to the next piezoelectric actuators 1 a to 1 h afterthe 70% charged state of the piezoelectric actuators 1 a to 1 h, towhich the drive voltage is applied.

Therefore, the start time, at which the drive voltage is applied to theplural piezoelectric actuator 1 a to 1 h, is sequentially delayed. Then,the period, during which the drive current of each of the piezoelectricactuators 1 a to 1 h becomes large, is averted, and the drive voltage isapplied to the next piezoelectric actuators 1 a to 1 h, with the drivecurrent reduced to a very small current that can be ignored.

Thus, the entire drive current is difficult to be increased, and theresistors R1 to R8 for current limitation inserted for eachpiezoelectric actuators 1 a to 1 d, can be reduced to a pair of commonresistors Ra and Rb, and the wiring is simplified, thereby easy toreduce the cost, and productivity is also improved.

Also, under the on-control state of a part of the piezoelectricactuators out of the plural piezoelectric actuators 1 a to 1 h, theon-control of the piezoelectric actuator 1 b to be on-controlled nextbecomes possible.

Therefore, while on-operation switch timing is reduced, thepiezoelectric actuators 1 a to 1 h are sequentially on-controlled, thusincreasing the operating speed of the plural piezoelectric actuators 1 ato 1 h in entirety, and improving the knitting speed of the knittingneedles of the knitting machine. In addition, the power consumption ofthe entire driver is hardly increased.

Specifically, the driver of the piezoelectric actuator of the presentinvention is capable of reducing the cost and improving the productivitythrough reducing the number of components and simplification of thewiring, and also realizing the increase in the switching operation speedof the plural piezoelectric actuators 1 a to 1 h.

Further, with the structure as described above, when switching betweenthe positive drive voltage and the negative drive voltage in each of thepiezoelectric actuators 1 a to 1 h, charging has already progressed inlarge quantity, to make it difficult that a large drive current flowstemporarily. Therefore, increase in the current in switching can beeffectively suppressed by the common resistors Ra and Rb pair.

In addition, in this invention, the switching operation timing of theplural piezoelectric actuators 1 a to 1 h by the controller 17 is notlimited to the point after the 70% charged state of the piezoelectricactuators 1 a to 1 h, but can be changed.

More specifically, when start of application of the drive voltage to thepiezoelectric actuators to be on-controlled next is after thepiezoelectric plates of the piezoelectric actuators 1 a to 1 h are putinto 70% charged state, the start of the application of the drivevoltage can be changed to the charging completion point where thepiezoelectric plates are put into 80% charged state, for example.Therefore, the switching control section 25 (controller 17) may beformed in accordance with the change in the switching operation timing.

A charging rate to the piezoelectric plate is the timing ofon-controlling one of the piezoelectric actuators 1 a to 1 h whileon-controlling any one of the piezoelectric actuators 1 a to 1 h, inwhich the drive current to each of the plural piezoelectric actuators 1a to 1 h becomes maximum immediately after the drive voltage is appliedand is thereafter transiently and drastically reduced. Therefore, evenif the charging rate is 60% or more, the object of the present inventioncan be achieved.

However, from the viewpoint of securing a stable operation withoutincreasing the power consumption so much, preferably the charging rateis set to be larger than 60%, that is, set to beyond 70%, and the timingto change in this state can be changed. Therefore, the switching controlsection 25 may be formed in accordance with the change in the switchingoperation timing.

Incidentally, as shown in FIG. 4, the driver of the piezoelectricactuator according to the present invention may be constituted byconnecting the phototransistors Q1, Q3, Q5, and Q7 to the positive sidefeeder line 19 through the terminal Sa of the common resistor Rb on theside opposite to the power supply section, and the phototransistors Q2,Q4, Q6, and Q8 are connected to negative side feeder line 21 through theterminal Sb of the common resistor Rb on the side opposite to the powersupply section. Other structure is similar to that of FIG. 1, and thesame effect can be obtained.

Incidentally, as described above, if the phototransistors Q1 to Q8 areconnected to the power supply section side of the common resistors Raand Rb in the positive side and the negative side feeder lines 19 and21, influence of variation of power supply voltage on thephototransistors Q1 to Q8 is reduced at switching the phototransistorsQ1 to Q8 (piezoelectric actuators 1 a to 1 h), thereby facilitating astable operation.

In addition, in the present invention, the piezoelectric actuator, towhich the drive voltage is applied and controlled, can be changed evenafter switching the drive power supply in an off-state.

Particularly, in the uniform piezoelectric actuators 1 a to 1 h, thepositive drive voltage and the negative drive voltage are switched, andthe uniform piezoelectric actuators 1 a to 1 h are bent and displaced ina vertical direction. In this structure, the phototransistors Q1 and Q2,Q3 and Q4, Q5 and Q6, and Q7 and Q8 connected in series are put into theon-state at switching, and a large drive current is easily flows.

In order to suppress the aforementioned situation, it is necessary toapply the drive voltage of reverse potential after the positive and thenegative drive voltage sufficiently drop by the off-operation. From thisviewpoint, it is effective to drive the power source after switched inthe off-state.

The aforementioned each of the piezoelectric actuators 1 a to 1 h isarbitrarily constituted, and for example, may be composed of onlypiezoelectric plates 3 and 5, or may have plural piezoelectric plates 3and 5 and the plates may be laminated, and also the supporting body isnot limited to the constitution of the aforementioned case 9.

According to the present invention, the switching mechanism of thecontroller 27 for switching the drive power source from the feeder linesto the plural piezoelectric actuators 1 a to 1 h, is not limited to theaforementioned combination of the light emitting diodes D1 to D8 and thephototransistors Q1 to Q8, but may be a contactless switch by onlytransistor for turning on and off the power source, and the switchingcontrol section 25 may be formed in accordance with the switchingmechanism.

Note that when the light emitting diodes D1 to D8 are combined with thephototransistors Q1 to Q8, an insulating state between the feeder lines19, 21, and the controller 17 side is easily formed and a stableoperation can thereby be realized.

Further, the power supply section 15 may also be arbitrarilyconstituted, may be constituted requiring both of positive voltage andnegative voltage, and may also be formed requiring either of thepositive voltage or the negative voltage to drive.

As described above, the present invention comprises:

plural piezoelectric actuators in which piezoelectric plates are stuckto plates;

a feeder line extending from a power supply section for applying a drivevoltage to the piezoelectric plate of each of the piezoelectricactuators;

a common resistor for current limitation connected in series to thefeeder line and limiting a drive current applied to the pluralpiezoelectric actuators to a prescribed range; and

a controller selectively and sequentially on-controlling the drivevoltage to be applied to each of the plural piezoelectric actuators fromthe feeder line,

wherein each of the piezoelectric actuators is connected to feeder lineof the common resistor on the side opposite to the power supply section,and the controller has a function to on-control the drive voltage to beapplied to the piezoelectric plate of the piezoelectric actuator to bedriven next, after the piezoelectric plate of the piezoelectricactuator, to which the drive voltage is applied, is put into a 60% ormore charged state.

Therefore, the driver of the piezoelectric actuator of the presentinvention has advantages of reducing the cost and improving theproductivity through reducing the number of components andsimplification of wiring, and realizing the increase in the switchingoperation speed of the plural piezoelectric actuators, and also reducingthe power consumption for the entire driver.

In addition, when the controller has the function to on-control thedrive voltage to be applied to the piezoelectric actuator to be drivennext, during applying the drive voltage to any one of the piezoelectricactuators, to which the drive voltage is applied, the switching speed ofthe plural piezoelectric actuators is further increased.

Further, the controller is connected to the power supply section side ofthe common resistors, and the drive voltage applied to the piezoelectricplate of the piezoelectric actuator is on-controlled. In thisconstitution, the controller is hardly affected by fluctuations in powersupply voltage at switching to the drive voltage applied to thepiezoelectric plate of the piezoelectric actuator, thus facilitating astable operation of the controller.

INDUSTRIAL APPLICABILITY

The driver of the piezoelectric actuator according to the presentinvention is not limited to the driver for driving the knitting needlesof the knitting machine as described above, but applicable as a drivesource mechanically moving a mechanical component directly or indirectlyconnected to each of the plural piezoelectric actuators havingpiezoelectric plates, such as an ink jet drive source and a dot wiredrive source in a printer.

1. A driver of a piezoelectric actuator in which a piezoelectric plateis stuck to a plate, comprising: plural piezoelectric actuatorsmechanically moving a mechanical component directly or indirectlyconnected to each of the piezoelectric actuators; a feeder lineextending from a power supply section for applying a drive voltage tothe piezoelectric plate of each of the piezoelectric actuators; a commonresistor connected to the feeder line in series, for current limitationlimiting a drive current to the piezoelectric plate of each of thepiezoelectric actuators to a prescribed range; and a controllerselectively and sequentially on-controlling the drive voltage to beapplied to each of the piezoelectric actuators by the feeder line,wherein each of the piezoelectric actuators is connected to the feederline of the common resistor on the side opposite to the power supplysection, and the controller has a function to on-control the drivevoltage to be applied to the piezoelectric plate of the piezoelectricactuator to be driven next, after the piezoelectric plate of thepiezoelectric actuator, to which the drive voltage is applied, is putinto a 60% charged state during applying the drive voltage to thepiezoelectric plate of the piezoelectric actuator.
 2. The driver of thepiezoelectric actuator according to claim 1, wherein the controller isconnected to the power supply section side of the common resistor, andhas a function to on-control the drive voltage applied to thepiezoelectric plate of the piezoelectric actuator.
 3. The driver of thepiezoelectric actuator according to claim 1, wherein the controllerincludes a switching mechanism for switching the drive voltage.
 4. Thedriver of the piezoelectric actuator according to claim 3, wherein theswitching mechanism includes a plurality of light emitting diodes and aplurality of phototransistors.
 5. The driver of the piezoelectricactuator according to claim 4, wherein emitters and collectors of theplurality of phototransistors are mutually connected in series anddisposed corresponding to the plurality of piezoelectric actuators. 6.The driver of the piezoelectric actuator according to claim 4, whereinpairs of the plurality of light emitting diodes are connected to aswitching control section.
 7. The driver of the piezoelectric actuatoraccording to claim 3, wherein the switching mechanism includes aplurality of transistors to control the drive voltage.
 8. The driver ofthe piezoelectric actuator according to claim 4, wherein when theplurality of light emitting diodes are combined with the plurality ofphototransistors, an insulating state between the feeder line andcontroller is easily formed.
 9. The driver of the piezoelectric actuatoraccording to claim 4, wherein joints of pairs of the plurality ofphototransistors are connected to common terminals of the plurality ofpiezoelectric actuators.